The long-term objectives of this research are to elucidate the role of the Sex-lethal gene in regulating reproductive behavior in Drosophila males and females and to understand the function of homosexual courtship in this species. Mutations in the Sex-lethal gene, which has a primary role in sex determination, affect diplo-X flies' ability to perform and elicit courtship. The proposed experiments will reveal the role of the Sex-lethal gene in regulating specific aspects of sex pheromone synthesis in females and the visual stimuli that are associated with attractive female flies. Other mutations in the Sex-lethal gene affect haplo-X flies' ability to discriminate between attractive and unattractive flies and to avoid the courtship of normal mature males. Experiments are proposed to identify aspects of sex pheromone synthesis that are regulated by the Sex-lethal gene in males and to identify female-specific Sex-lethal transcripts that interfere with males' ability to distinguish attractive females from unattractive males. Other experiments are proposed to analyze experience-dependent courtship modification, a phenomenon that has apparently evolved to limit the performance of reproductively wasteful homosexual courtship in this species. One set of experiments will reveal the stimuli that a courting male must perceive for experience-dependent courtship modification. In addition, parts of the nervous system that must function normally for a male's homosexual courtship to be limited will be revealed by analysis in genetic mosaics of the silver mutation, which affects courting males' ability to limit their homosexual courtship. Finally, the extent to which homosexual courtship and mechanisms for limiting its occurrence are characteristic of the genus will be determined by monitoring the behavior of other Drosophila species. These experiments will further our understanding of reproductive behavior in insects, which has obvious implications for biological control of agricultural pests.